It's been a process leading to that moment, a moral decline that's been going for several seasons now. A big scene for me is when he didn't save Jane in season 2 and justified it to himself by saying he was protecting Jesse from her negative influence and the drugs. But really, his main motive was that he was jealous over her control of him and wanted to continue to use and manipulate him (as he's been doing for the bulk of the five seasons).

I thought he let her die because she threatened to tell his wife. She was a liability.

I don't even know if Walt's been in much of a moral decline. He's shown more willingness to get his own hands dirty, and more confidence in his criminal pursuits, but his perception of right and wrong hasn't changed that much. Right, to him, is what benefits him. There's not much he thinks of as wrong. Even in the episodes when he's shown compassion it's usually so he can manipulate someone else. I don't know that he was on a moral high ground to begin with.

There's no real reason Saul couldn't have done it himself. Saul could have sent Bill Burr's character, even. If Jessie and Walt hadn't been in Saul's office at that exact time then Saul would have taken care of it. So, yeah. Strained.

Again, I agree more than I disagree. Shortcuts were taken, and the logic was forced (strained, as you say). But it wasn't the worst example of that kind of the thing in the show's history.

I liked - or rather WANTED to like - a lot of the episode, so I'm benefit-of-the-doubting. Straining myself, it make it work better in my mind.